Author Topic: LED Driver for Vision Engineering Lynx Dynascope C-073? + teardown  (Read 4112 times)

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Offline alex912Topic starter

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Can anyone recommend an off-the-shelf LED driver ~30V ~55W with PWM control, supporting an external thermistor, and ideally also with aux 12V output?

I have a Vision Engineering Lynx Dynascope 14-point LED light source (C-073) which needs a power supply. I'm new to LED drivers, so I'm probably missing a lot here. I'd love to find an off-the-shelf driver that can drive these LEDs, dim them easily, integrate with the existing thermistor in the heatsink, and even supply 12V to drive the fan. Ultimately driving the LEDs safely with dimming is the most important thing, so the other features are just nice-to-have.

The LED datasheet says that the forward voltage is 3.03-4.47V (3.7V typ) @ 700mA, and 3.9V @ 1000mA. It says the absolute max current is 1000mA, and that "Proper current derating must be observed to maintain junction temperature below the maximum". There are 2 strings of LEDs, each with 7 LEDs in series.

How do I spec out an LED driver for these?
  • I assume I need a constant-current driver with user-settable output current?
  • Can I use a driver with an absolute minimum voltage that's higher than the LED string forward voltage of ~27V?
  • Does this mean I can drive them at 1000mA but only as long as the temperature stays reasonable? Or should I just only plan on driving them to 700mA as a max?
  • For one string of 7 LEDs in series, I need a driver capable of outputting at least 3.9V*7=27.3V and 1000mA.
  • For two strings in parallel, >=27.3V @ 2000mA =~ 55W driver.

I've found a few possible candidates, but I'm not sure if I'm going down the wrong path:
Any help would be very appreciated. Thanks!

-----

Teardown & reverse engineering pics follow, in case it might help anyone in the future. I may have made mistakes here, so no guarantees! :)

The unit comprises 14 LEDs total, split into 2 strings each with 7 LEDs in series. The LEDs are attached to a metal heatsink with a thermistor and a fan. The casing also holds a glass dome lens over each LED, to focus the light for use with a particular magnification microscope (this LED model says "0.7x  0.5x/0.3x").

The LEDs are Luxeon III Star White Lambertian LXHL-LW3C. I believe these star boards use the Luxeon III Emitter LXHL-PW09. 65lm @ 700mA.
https://www.luxeonstar.com/lxhl-lw3c-white-luxeon-iii-star-led-65lm

The unit has a female 8-pin connector on it, for which I think the correct male connector is ODU S21M07-P08MFD0 (which go for $20 each new!). I found what I think are compatible connectors on ebay/aliexpress searching for "medical plastic connector". There's no set pinout for these connectors, so I numbered the pins arbitrarily in the attached pinout pic.
https://www.mouser.com/datasheet/2/941/MEDI-SNAP_S21M07-P08MFD0-657S-1634717.pdf

The thermistor is probably a Pt100 PTC. I measured it at ~112ohm @ 25C, and ~119ohm @ 40C. My measuring setup might have added a bit of resistance, but otherwise this seems to line up with the Pt100 table.

The fan is 50mm, 12V @ 0.15A


« Last Edit: January 31, 2021, 06:48:35 pm by alex912 »
 
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Offline ocset

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Re: LED Driver for Vision Engineering Lynx Dynascope C-073? + teardown
« Reply #1 on: January 31, 2021, 06:51:08 pm »
Quote
Can I use a driver with an absolute minimum voltage that's higher than the LED string forward voltage of ~27V?
Sorry no.
You could look at offtheshelf offerings from meanwell, recom, osram, philips,  and tdk etc.

I doubt youll get an offtheshelf'er that can use the thermistor input.  Use a micro in a separate module to read the thermistor, and dim the offtheshelf driver down accordingly. Eg, use an arduino board to do this if you want. They are easy to program with youtube video help.

You must be very careful about plugging the leds into a driver thats powered up but on no_load...because its vout may well be at the overvoltage threshold, and so when you connect your led string to the vout, then a large surge of current will flow through your leds from the output   capacitor of the led driver. But you can get round this by using a led driver which senses open load, and then shuts down...until its power is recycled say.....or you could just remember to only power the led driver up when the led load is actually already connected.

Its best to stick to the datasheet max led current...but if you can keep the led junction less than 85 degrees, then drive them at any current you want.
Use k type thermocouples on the heatsink right next to   the led to get an idea what the led junction temp is. The led datasheet will give you the thermal resistance from led junction to case.......then estimate the thermal resistance from led case to heatsink...then work out led junction temp from that.
« Last Edit: January 31, 2021, 06:59:56 pm by treez »
 

Offline alex912Topic starter

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Re: LED Driver for Vision Engineering Lynx Dynascope C-073? + teardown
« Reply #2 on: February 01, 2021, 01:32:08 am »
Thanks for the detailed reply, treez!


Its best to stick to the datasheet max led current...but if you can keep the led junction less than 85 degrees, then drive them at any current you want.
The datasheet says forward voltage is 3.03V-4.47V (3.7V typical) @ 700mA, and 3.9V typical @ 1000mA (which is the absolute max current).
Do I care at all about the Vf min/max when spec'ing out a driver, or do I just care about the Vf typical at a certain current?

If I put the 2 7-LED strings in parallel, that gives me 25.9V Vf typical @ 1400mA, and 27.3V Vf typical @ 2000mA.
Looking at this Meanwell CV+CC driver, do either of these seem appropriate?

Meanwell HLG-60H-24-AB:
  • DC Voltage: 24V
  • Constant current region: 14.4 ~ 24V
  • Voltage Adj Range: 22 ~ 27V
  • Current Adj Range: 1.5 ~ 2.5A
  • Over Voltage Protection: 28 ~ 35V
Meanwell HLG-60H-30-AB:
  • DC Voltage: 30V
  • Constant current region: 18 ~ 30V
  • Voltage Adj Range: 27 ~ 33V
  • Current Adj Range: 1.2 ~ 2A
  • Over Voltage Protection: 35 ~ 43V


You must be very careful about plugging the leds into a driver thats powered up but on no_load
I'll definitely keep the no load issue in mind -- good to know!


Use a micro in a separate module to read the thermistor, and dim the offtheshelf driver down accordingly..
...
Use k type thermocouples on the heatsink right next to   the led to get an idea what the led junction temp is. The led datasheet will give you the thermal resistance from led junction to case.......then estimate the thermal resistance from led case to heatsink...then work out led junction temp from that.
Makes sense -- I'll look into this
 

Offline nexus

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Re: LED Driver for Vision Engineering Lynx Dynascope C-073? + teardown
« Reply #3 on: August 09, 2022, 10:13:10 pm »
Hey any updates on this? I just picked up a C-073 ring light and was wondering if you ever completed this project. Lots of useful info including the pinouts and power requirements; thank you for that! Also, did you happen to get a pic of the fan model #? The unit I bought does not include the fan for the lights.
 

Offline alex912Topic starter

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Re: LED Driver for Vision Engineering Lynx Dynascope C-073? + teardown
« Reply #4 on: August 09, 2022, 10:28:14 pm »
Glad it was helpful!

I did a bunch of research on off-the-shelf power supplies, and I did find a few that were reasonable. Unfortunately I don't have any of those details anymore. I ended up finding the actual power supply for a reasonable price, so that was a much easier route.

It's hard to see the fan label, but I think it says: BI Sonic SP501512M 01 12V 0.15A
 
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Offline nexus

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Re: LED Driver for Vision Engineering Lynx Dynascope C-073? + teardown
« Reply #5 on: August 10, 2022, 12:20:09 am »
Thank you for that extra info once again. If I don't find the correct power supply and end up building my own to run the light, I will definitely share the design.
 

Offline nexus

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Re: LED Driver for Vision Engineering Lynx Dynascope C-073? + teardown
« Reply #6 on: October 01, 2022, 05:55:16 pm »
So a little update. Decided to make a project out of the C073 ring light power supply.

Designed a board around the PIC16F1946. It's a little overkill but it is in stock, unlike many other pic parts.

Uses the MPM6010GQVE which is a synchronous step-down LED driver. 33VDC is provided by a traco TPI 180-136-M.
Also threw in a MAX31865 to read the RTD and monitor LED temp.

Also designed a custom enclosure. Going to see if PCBWAY can do it with their sheet metal service. They've come through before.

We'll see how the programming goes. Done similar thingies with PIC16 so hopefully no surprises.
 

Offline nexus

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Re: LED Driver for Vision Engineering Lynx Dynascope C-073? + teardown
« Reply #7 on: November 06, 2023, 06:49:50 am »
Circling back after a while. I got rev 1 of my project working fairly well. Not perfect, but certainly functional!



Project files (BOM, gerbers, firmware) available here: https://neonkev.com/2023/11/06/vision-engineering-lynx-microscope-c073-led-ring-light-custom-power-supply/

 


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